In the fabrication of semiconductor devices, there is a need to perform chemical mechanical polishing (CMP) operations and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the wafer level, transistor devices having diffusion regions are formed. In subsequent levels, metal interconnect lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further interconnect and dielectric layers becomes substantially more difficult due to the higher variations in the surface topography. In semiconductor manufacturing processes, metal interconnect patterns are formed in a dielectric material on a wafer, and then, chemical mechanical planarization, CMP, operations are performed to remove the excess metal. After any such CMP operation, it is necessary that the planarized wafer be cleaned to remove particulates and contaminants.
In the manufacture of electronic devices such as integrated circuits, the presence of particulate contamination, trace metals, and mobile ions on a wafer is a serious problem. Particulate contamination can cause a wide variety of problems such as localized corrosion, scratching, and “shorts” in the integrated circuit. Mobile ion and trace metal contaminants can also lead to reliability and functional problems in the integrated circuit. The combination of these factors results in lower device yields on a wafer, thereby increasing the cost of an average functional device on the wafer. Each wafer, being at different stages of fabrication, represents a significant investment in terms of raw materials, equipment fabrication time, and associated research and development.
Chemical-mechanical polishing (“CMP”) is a commonly used technique for planarizing a film on the wafer prior to subsequent processing of the wafer. CMP usually involves the introduction of a polishing slurry having 50-100 nanometer sized abrasive particles onto the surface of a polishing pad. The wafer with the layer of material, dielectric or metal, to be removed is placed against the surface of a polishing pad with a slurry. Rotating the wafer against the rotating polishing pad decrease the thickness of the layer through a combination of chemical and mechanical actions. The slurries typically are water based and can include fine abrasive particles such as silica, alumina, and other metal oxide abrasive materials. After polishing is complete, the processed wafers must be cleaned to completely remove residual slurry and other residue from the polishing process. The surface is the ready for other processing steps such as electrochemical deposition, etching, and photolithography.
To clean residual slurry material from the surface of the polished surface, especially particles less than 0.1 microns in diameter, cleaning brushes are commonly used. These cleaning brushes are usually cylindrical in shape and are rotated along a center axis of the brush. The cleaning brushes are also often made of a foam or porous polymeric material such as polyvinyl alcohol (“PVA”). The combination of rotational movement of the brush and force or pressure placed on the brush against the wafer as well as the application of cleaning fluids or deionized water causes residual slurry materials to be removed from the surface of the wafer.
These brushes have protrusion or nodes on their surface for contact and material removal from a substrate. Brushes are formed as sleeves and are slid over a core support which is used to deliver fluids to the brush and to rotate the brush. After extended use, the brush is replaced with a new brush sleeve and requires the polishing tool be stopped adding to lost productivity and downtime. Alignment of the brush protrusions along the brush core is important for consistent contact of the brush with the substrate. Asymmetric alignment and distortion of the spacing of the nodes on the sleeve is a problem with sleeve replacement. Newly installed brushes must be broken in, flushed, and gapped prior to cleaning product substrates. Often time dummy wafers are used to ensure the cleanliness, and operational stability including dimensional, rotational and contact of the brush with the dummy wafers. This non-value added step is costly for manufactures in time and dummy wafers.
To perform the cleaning operations in an automated manner, fabrication labs employ cleaning systems. The cleaning systems typically include one or more brush boxes in which wafers are scrubbed. Each brush box includes a pair of brushes, such that each brush scrubs a respective side of a wafer. To enhance the cleaning ability of such brush boxes, it is common practice to deliver cleaning fluids through the brush (TTB). TTB fluid delivery is accomplished by implementing brush cores that have a plurality of holes that allow fluids being fed into the brush core at a particular pressure to be released onto the substrate surface. The fluid is distributed from the brush core through the polymeric material and onto the substrate surface. Ideally, the chemicals flow through the bore and then flow out of the core at an equal rate from all of the brush core holes. It has been found that the chemicals delivered to the core are not flowing out of all of the holes at the same or substantially the same rate and that brush core holes near the chemical receiving end usually flow out chemicals at a substantially faster rate than holes at the opposite side of the chemical receiving end.
As semiconductor feature sizes decrease and device performance requirements continue increase, cleaning engineers are also challenged to improve their associated processes. To meet these demands, the same cleaning equipment is now being used to perform operations other than basic de-ionized (DI) water cleaning. Such operations include the application of sophisticated chemicals to remove particulates and/or to etch precise films of materials from the surfaces of a wafer. Many cleaning systems are now required to also apply reactive chemicals, such as hydrofluoric acid, uneven application will have a severe impact on the wafer being processed. For instance, if more HF is applied to one part of the wafer and less is applied to another part of the wafer, the surface of the processed wafer may exhibit variations in the amount of film removed across the wafer.